ASK THE EXPERTS: Bad Modules or Bad Design?

Intermediate

I have three, four-module strings feeding a single charge controller. Two of the strings are in full sun all day while the third is partially shaded early in the morning. The third string was installed later and uses a different brand of module than the first two.

I have now had two of the modules in the shaded string fail. Is it possible I have a bad batch? I think it more likely that my understanding is faulty in thinking that modules are immune to damage by shading, open or short circuits, and reasonable external voltages. 

Donald Wood • via e-mail

Ordinary shading from trees or buildings will not cause modules to fail. You likely ran into a bad batch of modules. Contact the manufacturer for warranty replacement.

Modules are designed to spend a lot of their time open circuit when systems are regulating, and no damage will occur. Short-term short circuits due to mis-wiring typically will not damage modules either. That said, array short circuits will not occur in properly installed arrays and it’s a situation you definitely want to avoid.

Joe SchwartzHome Power

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